Save Luke

题意翻译

****题意****: 现在,有个人站在一条路宽度为 d 的马路上,这条路有两个压路机,而这个人在两个压路机左右端点的中间,两个压路机的移动速度为 v1 和 v2 ,距离为 l ,人可以在两个压路机中间左右任意位置,求人最多的存活时间。 ****输入格式****: 按顺序输入宽度、距离和两辆压路机的速度,即 d、l、v1、v2。 ****输出格式****: 这个人最多存活的时间,保留小数点后20位。 由 @是qjx呀 提供。

题目描述

Luke Skywalker got locked up in a rubbish shredder between two presses. R2D2 is already working on his rescue, but Luke needs to stay alive as long as possible. For simplicity we will assume that everything happens on a straight line, the presses are initially at coordinates $ 0 $ and $ L $ , and they move towards each other with speed $ v_{1} $ and $ v_{2} $ , respectively. Luke has width $ d $ and is able to choose any position between the presses. Luke dies as soon as the distance between the presses is less than his width. Your task is to determine for how long Luke can stay alive.

输入输出格式

输入格式


The first line of the input contains four integers $ d $ , $ L $ , $ v_{1} $ , $ v_{2} $ ( $ 1<=d,L,v_{1},v_{2}<=10000,d&lt;L $ ) — Luke's width, the initial position of the second press and the speed of the first and second presses, respectively.

输出格式


Print a single real value — the maximum period of time Luke can stay alive for. Your answer will be considered correct if its absolute or relative error does not exceed $ 10^{-6} $ . Namely: let's assume that your answer is $ a $ , and the answer of the jury is $ b $ . The checker program will consider your answer correct, if ![](https://cdn.luogu.com.cn/upload/vjudge_pic/CF624A/259203790d90e969d73ec841bd0673c1e8e7d69a.png).

输入输出样例

输入样例 #1

2 6 2 2

输出样例 #1

1.00000000000000000000

输入样例 #2

1 9 1 2

输出样例 #2

2.66666666666666650000

说明

In the first sample Luke should stay exactly in the middle of the segment, that is at coordinates $ [2;4] $ , as the presses move with the same speed. In the second sample he needs to occupy the position ![](https://cdn.luogu.com.cn/upload/vjudge_pic/CF624A/99faa0f5fe57ec6bb39344749c7bc94bcc24c476.png). In this case both presses move to his edges at the same time.